The torrential, early December rain fell on top of already saturated soil from an especially wet and persistent monsoon season, thanks to El Nino, which amplified the flooding to catastrophic levels. Water rose chest-deep in city streets, power was shut off and the airport was closed.
Nearly 300 people have been reported dead in floods since the heavy monsoon rain began in early November. Thousands have been displaced.
On Dec. 8, satellite company Digital Globe collected new imagery of the affected areas in southeast India. With standing water still covering the ground, the area around Chennai may not dry out for weeks or even months.
The India monsoon has two phases, the summertime southwest monsoon and the wintertime northeast monsoon. “For most of the nation, the northeast monsoon has a drying effect, since the winds are bringing cool, dry air from interior Asia,” writes Bob Henson at Weather Underground. “But as the northeasterlies pass over the Bay of Bengal during autumn, they pick up moisture that is often deposited across far southeast India. Chennai typically receives more than half its moisture this way.”
During particularly strong El Ninos, the southwest monsoon can become much drier than average, but it has the opposite affect on the northeast monsoon. In an average year, Chennai receives around 55 inches of rain. This year, amid one of the top-3 strongest El Ninos on record, Chennai will end with well over 60 inches in just November and December alone.